Ajax Please wait image using update panel in asp.net c#

<asp:UpdateProgress ID="UpdateProgress" runat="server">
<ProgressTemplate>
<asp:Image ID="Image1" ImageUrl="~/Images/loading.gif" AlternateText="Processing" runat="server" />
</ProgressTemplate>
</asp:UpdateProgress>

<asp:ModalPopupExtender ID="modalPopup" runat="server" TargetControlID="UpdateProgress"
PopupControlID="UpdateProgress" BackgroundCssClass="ModalPopupBG" />

<script type="text/javascript">
    //*****************************Model popup (Please wait)****************

    var prm = Sys.WebForms.PageRequestManager.getInstance();
    prm.add_beginRequest(BeginRequestHandler);
    prm.add_endRequest(EndRequestHandler);
    function BeginRequestHandler(sender, args) {
        var popup = $find('<%= modalPopup.ClientID %>');
        if (popup != null) {
            popup.show();
        }
    }

    function EndRequestHandler(sender, args) {
        var popup = $find('<%= modalPopup.ClientID %>');
        if (popup != null) {
            popup.hide();
        }
    }

</script>